Cystic Fibrosis (CF) is a disease characterized by chronic airways obstruction and infection. It is the most common life threatening genetic disease of the Caucasian population with its major risks resulting from damage to the lungs. In CF, a mutation (defect) in a protein called CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) makes transport of water, sodium and chloride in airway cells abnormal. This results in thickened airway secretions that obstruct airways and predispose patients to chronic bacterial infection. CPX is a compound which may act as a "protein-repair" agent, helping to restore function of CFTR in patients with CF. Repairing the defective CFTR protein may improve the transport of chloride and water out of airway cells, making secretions less thick, less sticky, and easier to cough out. The purpose of this study is to evaluate the safety and pharmacokinetics (blood and urine tests to evaluate how quickly a drug is absorbed into the blood stream and eliminated from the body) of a specific dose of CPX. Participants in the study will receive 100 mg of CPX four times a day for a total of 24 doses.